Sear device for an automatic firearm



Jan. 8, 1957 E. c. LEE

SEAR DEVICE FOR AN AUTOMATIC FIREARM Filed Dec. 31. 1953 3 Sheets-Sheet1 IIZI IN V EN TOR.

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Jan. 8, 1957 E. c. LEE

SEAR DEVICE FOR AN AUTOMATIC FIREARM 3 Sheets-Sheet 2 Filed Dec. 51,1953 E E mL M- m. m E

Jan. 8, 1957 E. c. LEE 2,776,600

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SEAR DEVICE FOR AN A ATIC FIREARM Filed Dec. 3l, 1953 I INVENTOR.E%wurfl.' ELLEE 1% a W4 62. MOQM United States Patent SEAR DEVICE FOR ANAUTOMATIC FIREARM Edward C. Lee, Detroit, Mich., assignor to the UnitedStates of America as represented by the Secretary of the ArmyApplication December 31, 1953, Serial No. 401,741

3 Claims. (Cl. 89-136) This invention relates to automatic firearmswherein a firing member is resiliently mounted for slidable movement ina reciprocating bolt and is particularly directed to means for securingthe firing member in a cocked position and for the release thereof whenthe belt is in a battery position.

In automatic firearms of the type described in Patent No. 1,628,226 toJohn M. Browning, there is provided a longitudinally reciprocating bolthaving a spring-biased firing member mounted for slidable movementbetween a forward firing position and a rearward cocked position. Thefiring member is arranged to be releasably retained in the cockedposition by a spring-biased sear reciprocably mounted in verticalslideways. When the bolt is moved to the battery position, the sear isactuated by suitable means to release the firing member which movesforwardly under the bias of its spring to discharge the chamberedcartridge. During the ensuing recoil movement of the bolt, a cockinglever pivotally mounted therein, moves the firing member rearwardlyready for engagement with the sear. During counter-recoil of the bolt,the cocking lever is counter-rotated permitting the firing member to bebiased slightly forward into releasable engagement with the sear and thebottom end of such cocking lever is swung free of the firing memberwhereupon the latter is free to move forwardly when released by the searto effect another cycle of operation.

In firing mechanisms of this type, considerable trouble has beenexeperienced with the sear prematurely releasing the firing memberwhereby the chambered cartridge is not fired because the firing memberdoes not strike the primer with sufiicient force to ignite it.

The conventional type sear is maintained in holding position only by thebias of its spring and there are no means provided to prevent the searfrom vibrating through the shocks produced during operation of thefirearm. Consequently, vibration of the sear while engaging the firingmember causes either faulty or mis-engagement and vibration duringengagement causes the firing member to be prematurely released.

Accordingly, it is an object of this invention to provide in anautomatic firearm a sear mechanism which holds the firing member inpositive engagement until actuated by a scar slide.

A further object of this invention is to provide in an automatic firearmbolt a pivotally mounted sear which reciprocates smoothly between afiring member holding position and a disengaged position.

It is the specific object of this invention to provide in an automaticfirearm bolt a slidably mounted sear slide which both locks the sear inthe firing member holding position and actuates the sear to disengagedposition.

The specific nature of the invention as well as other objects andadvantages thereof will clearly appear from a description of a preferredembodiment as shown in the accompanying drawings in which:

Fig. 1 is a longitudinal cross-sectional view of a firearm bolt showingthe firing member in retracted position;

Patented Jan. 8, 1957 Fig. 2 is a fragmentary view similar to Fig. 1 butshowing the firing member in the fire position;

Fig. 3 is an end view of the bolt partially cross-sectioned to show themounting of the sear slide and sear slide actuator;

Fig. 4 is an enlarged exploded view of the sear mechanism;

Fig. 5 is. an enlarged fragmentary perspective view of the searslideshowing the sear actuating cam surfaces;

Fig. 6 is a view taken along line 6-6 of Fig. 1 showing the sear inlocked firing member holding position;

Fig. 7 is a View similar to Fig. 6 but showing the sear unlocked andinitially contacted by the sear slide for rotation thereof; and

Fig. 8 is a view taken along line 8--8 of Fig. 2 showing the searactuated to firing member disengaged position. 1

Shown in the figures is a bolt 12 of the well-known Browning type inwhich there is provided a longitudinal channel 13 and a forwardlyextending bore 14 and counterbore 15. A sear 16 of bell crankconfiguration is mounted in channel 13 as hereinafter described forpivotal movement between a holding position and a disengaged position.Mounted for slidable movement in bore 14 and counterbore 15 is a firingmember 17 which is reciprocable between a firing and a retractedposition. Firing member 17 is essentially of conventional type, beingprovided with a striker portion 18, a. hollow extension portion 19,which houses a compressible spring 20, and a forwardly facing hookportion 21 which projects downwardly from a slabbed portion 22 locatedat the rear end of such extension portion. In addition, there isprovided a tongue portion 23 which extends rearwardly from hook 21Provided in the upper side of bolt 12 is a recess 24 which communicateswith counterbore 15 by means of a vertical slot 25. Mounted in recess 24is a cocking lever stop member 26 having a pin portion 27 which extendsdownwardly through a hole 28 to be received by an elongated slot 29 inextension 19. The rear end of spring 20 is arranged to bear against pin27 whereby firing member 17 is biased to the firing position.

A cocking lever 30 is mounted in slot 25 on a transverse pin 31. The endof cocking lever 30, extending below pin 31, is receivable by slot 29and is arranged to be engageable with the rear end thereof. The upperend of cocking lever 30 is receivable in a V-slot 32 provided in a topplate bracket 34 of the firearm during initial recoil and is slidablyengageable thereafter with the underside of the top plate bracket duringthe remainder of the recoil. Thereby, cocking lever 30 is pivoted inclockwise direction to actuate firing member 17 against the bias ofspring 20 to the retracted position and holds the firing member in suchretracted position until pivoted in counter-clockwise direction. Duringcounter-recoil of bolt 12, the top end of cocking lever 30 reengageswith V-slot 32 whereby such cocking lever is pivoted in counterclockwisedirection, permitting firing member 17 to be biased by spring 20slightly forward for cocked engagement with sear 16, as hereinafterdescribed, and the bottom end swung free of slot 29.

Sear 16, as has hereinbefore been described, is of bell crankconfiguration and is comprised of a longitudinal foot portion 35 and avertical leg portion 36. A lateral hole 33 extends through sear 16 atthe junction of foot portion 35 with leg portion 36 and receives a pin37 whereby the sear is mounted for pivotal movement. Provided in the topside of foot portion 35 is a lateral indent portion 38 which forms arearwardly facing engaging surface 39 cooperable with hook 21 forreleasably holding firing member 17 in a cocked position. Indent 38,further, is arranged to receive tongue 23 when firing member 17 is inthe retracted and cocked positions and the top side of foot portion 35,forwardly of engaging surface 39, is arranged to be slidably engagedwith the underside of tongue 23 when firing member 17 reciprocatesbetween cocked and firing positions. Provided in the bottom side ofchannel 13 is a well which receives one end of a compressible spring 41.The opposite end of spring 41 bears against the bottom side of footportion 35 whereby sear 16 is biased to the holding position.

Located laterally through the upper portion of leg 36 is a cylindricalbore 42 having an upwardly extending opening formed by a front and rearlaterally arranged lip portion, noted by 44 and 45 respectively.Projecting forwardly from rear lip 45 is a lug 46. Extending forwardlyand outwardly from front lip 44 and the adjoining portion of bore 42, asbest shown in Fig. 4, are similar right and left vertical cam surfaces,noted by 47 and 48 respectively.

Provided laterally through bolt 12 is a cylindrical bore 50 arranged tointersect the upper portion of channel 19. A cylindrical sear slide 51is reversibly mounted for slidable movement in bore 50 and is adapted tocooperate with lug 46 and cam surfaces 47 and 48, as hereinafterdescribed. Sear slide 51 is recessed, as noted by 52 and best shown inFig. 5, so as to form spaced apart angular actuating surfaces 53 andsimilar actuating surfaces 54 angularly related thereto. Provided insear slide 51, opposite recess 52, is a mortise 61. Recess 52 andmortise 61 are located in sear slide 51 away from the longitudinalcenter thereof so as to establish a long portion 55, which is engageableby a trigger mechanism (not shown) when installed in either the right orthe left side of bolt 12, and a short portion 56. When sear slide 51 isassembled for operation from the right side of bolt 12, actuatingsurfaces 53 are arranged to cooperate with cam surfaces 47 and 48 andwhen assembled for operation from the left side, actuating surfaces 54cooperate with such cam surfaces. Sear slide 51 is secured againstrotation by sear slide actuator 62 which is slidably mounted in avertically disposed cylindrical hole 71 to transverse the sear slide ashereinafter described. A cup-like member 57 is installable in bore 50 soas to be adjacent short portion 56 and is secured in position by a pin58 which is receivable by one of a pair of opposed holes 59 providedtherein. A spring 60 is received by member 57 and is arranged to bearagainst the end of short portion 56 to bias sear slide 51 away to a searlocking position.

When assembled in bolt 12 for operation from the right side, sear slide51 is biased by spring 60 so that the left one of the actuating surfaces53 engages with cam surface 48. At the same time, lug 46 is engageablewith the cylindrical surface of sear slide 51 whereby sear 16 is blockedagainst pivoting from holding position. To

actuate sear 16 from holding to disengaged position, long portion 55 ispressed inwardly. At the point where the right one of actuating surfaces53 engages the mating cam surface 47, mortise 61 is moved adjacent lug46, unblocking sear 16. Consequently, when further movement of actuatingsurface 53 against cam surfaces 47 moves the top side of leg portion 36forwardly, pivoting foot portion 35 downwardly to disengage firingmember 17, lug 46 is received by mortise 61. When sear slide 51 isassembled for operation from the left side of bolt 12, the right one ofactuating surfaces 54 is biased into normal engagement with the matingcam surface 47 and the camming engagement of the left one of actuatingsurfaces 54 with the mating cam surface 47 moves the unblocked sear 16to disengaged position.

As has hereinbefore been recited, sear slide 51 is transversed by searslide actuator 62 which secures the sear slide against rotation and isalso the means of actuating sear 16 from the top side of bolt 12. Searslide actuator 62 is comprised of a cylindrical portion 65 from whichthere extends downwardly a portion 66 substantially of elongatedrectangular cross section. Intermediate one of the narrow sides ofportion 66 is a ramp 67 which inclines downwardly and inwardly to forman extending guide portion 68 of smaller dimension. Guide 68 is slidablyreceived in a suitable opening below bore 50.

An elongated hole 69 is provided in sear slide 51 on each side of recess52, one of which is arranged to slidably receive portion 66 of scarslide actuator 62 whether sear slide 51 is assembled from the right orleft side of bolt 12. Provided in each hole 69 is an angular side 70engageable by ramp 67 whereby sear slide 51 is cammable to actuate sear16 when a vertical force is applied to sear slide actuator 62. It hasbeen brought out that when reversed in bolt 12, sear slide 51 also hasto be rotated to have the opposite ones of actuating surfaces 53 or 54cooperable with the cam surfaces 47 and 48. Consequently, angular side70 has to be located oppositely in the holes 69 making it necessary forsear slide actuator 62 to be rotated to have ramp 67 engageabletherewith. Provided in cylindrical portion 65 is a pair of grooves 75,one of which is engageable with an arm portion 76 of clocking lever stopmember 26 to limit the movement of sear slide actuator 62 in whicheverposition sear slide actuator 62 is installed.

To assemble sear 16 in bolt 12, the sear is placed in channel 13 andsear slide 51 then assembled through bolt 12, transversing sear 16through bore 42. Sear 16 is then depressed against spring 41 until themounting pin 37 can be assembled through hole 33 whereby sear slide 51is properly positioned between lips 44 and 45.

When a firearm incorporating the sear mechanism of this invention is tobe fired, a trigger mechanism (not shown) either presses downwardly onsear slide actuator 62, which actuates sear slide 51 by the cammingengagement of ramp 67 thereon with the mating angular side 70 in thesear slide, or inwardly on the end of long portion 55 of scar slide 51if operation from the side of the firearm is desired.

If the sear mechanism is arranged for operation from the right side ofthe firearm, the left one of actuating surfaces 53 in sear slide 51 isin resilient engagement with cam surfaces 48 in sear 16 when the firearmis in battery. When the trigger mechanism (not shown) presses sear slide51 inwardly to fire the firearm, the initial movement of the sear slidemoves mortise 61 in position to receive lug 46 and then engages theright one of actuating surfaces 53 with the mating cam surface 47.Continued movement of scar slide 51 causes leg portion 36 of scar 16 tobe moved forwardly by the camming engagement of actuating surface 53with cam surface 47. As sear 16 is bell crank in configuration andoperation, the forward movement of leg portion 36 moves foot portion 35downwardly causing engaging surface 39 to move out of engagement withhook 21 of firing member 17 which is then free to be urged forwardly byits spring 20 to fire the chambered cartridge. During the forward travelof firing member 17, the bottom sides of book 21 and tongue 23 slidablyengage the top side of foot portion 35 forwardly of engaging surface 39,thereby holding sear 16 in the disengaged position.

During the ensuing recoil of bolt 12, the top end of cocking lever 39 isreceived by V-slot 32 causing the lower end to engage the end of slot 29in extension 19 for actuation of firing member 17 to retracted position.Firing member 17 is maintained in retracted position during theremainder of the recoil by the engagement of the top end of cockinglever 30 with the bottom side of top plate bracket 34. When hook 21 ismoved rearwardly of engaging surface 39, sear 16 is free to be biased toholding position by spring 41 with the hook 21 and tongue portion 23being received by indent 38. As sear 16 moves to holding position, camsurface 47 is moved forwardly permitting sear slide 51 to be biased byspring 60 to lock position wherein sear 16 is blocked against movementfrom holding position by the engagement of the surface of sear slide 51.with lug 46. During counter-recoil of bolt 12, the top side of cockinglever 30 is again received by V-slot 32 causing the cocking lever topivot and thereby permit firing member 17 to be biased forwardly byspring until stopped in cocked position by the engagement of hook 21with the engaging surface 39. During the impact of engagement and theremainder of the travel of bolt 12 to battery, sear 16 is blockedagainst movement away from holding position, by the means already explained, and thereby there is prevented any chances of firing member 17being prematurely released.

It is readily apparent from the foregoing that there is here provided asuperior sear mechanism of sturdy, easily fabricated construction inwhich the sear moves smoothly between a holding and a disengagedposition and securely holds the firing member against premature release.

Although a particularly embodiment of the invention has been describedin detail herein, it is evident that many variations may be devisedwithin the spirit and scope thereof and the following claims areintended to include such variations.

I claim:

1. In a firearm bolt, a sear having a leg portion and a foot portionextending at right angles therefrom, said leg portion being providedwith a lateral opening and said foot portion being provided with arearwardly facing engaging surface in the upper side thereof, pin meansmounted through said sear to provide for pivotal movement of said searabout the junction of said leg portion and said foot portion, springmeans for biasing said sear from a disengaged to a holding position, acam portion extending rearwardly into said opening, a lug portionextending forwardly into said opening, a reciprocal firing memberspringbiased from a retracted to a firing position, hook means extendingfrom said firing member, said hook means being engageable by saidengaging surface when said sear is in said holding position whereby saidfiring member is releasably held in said retracted position, acylindrical sear slide slidably mounted in a bore in the bolt forreception by said opening, said sear slide being provided with a mortiseand a recess having angular actuating surfaces, said sear slide beingactuatable from a sear actuated position to a sear locked positionwherein said lug is engageable with said sear slide to block said searin said holding position, and said actuating surfaces being cooperablewith said cam portion for actuating said sear to said disengagedposition when said sear slide is moved to said sear actuated positionand said mortise is in position to receive said lug.

2. In a firearm bolt, a sear having a leg portion and a foot portionextending at right angles therefrom, said leg portion being providedwith a lateral opening and said foot portion being provided with arearwardly facing engaging surface in the upper side thereof, pin meansmounted through said sear to provide for pivotal movement of said searabout the junction of said leg portion and said foot portion, springmeans for biasing said sear from a disengaged to a holding position, acam portion extending rearwardly into said opening, a lug portionextending forwardly into said opening, a reciprocal firing memberspring-biased from a retracted to a firing position, hook meansextending from said firing member, said hook means being engageable bysaid engaging surface when said sear is in said holding position wherebysaid firing member is releasably held in said retracted position, aspring-biased cylindrical sear slide slidably mounted in a bore in the:bolt for reciprocation in said opening between a sear locked positionand a sear actuated position and being normally engageable by said lugwhereby said sear is blocked in said holding position, said sear slidebeing provided with a recess having angular end walls cooperable withsaid cam portion for actuation of said sear to said disengaged position,a hole on each side of said recess and a mortise for receiving said lugwhen said sear slide is away from said sear locked position whereby saidsear is pivoted to said disengaged position, angular sides in saidholes, and a cylindrical actuator member slidably received in either oneof said holes for securing said sear slide against rotation, saidactuator being provided with a ramp portion selectively cooperable withsaid angular sides whereby a vertical force applied against saidactuator member is translated to lateral movement of said sear slide.

3. In a reciprocating firearm bolt, a reciprocable firing memberspring-biased from a retracted to a firing position, lever means forretracting said firing member responsive to recoil of the bolt, a searof bell crank configuration pivotally mounted on a centrallytransversing pin, cooperating latch means on one arm of said sear andsaid firing member for releasably latching said firing member in saidretracted position, a lip on the other arm of said sear provided with atriangular-like cam portion, a transverse cylindrical sear slideslidably mounted in a bore in the bolt, said sear slide having anactuating end portion extendable from the bolt and being reversiblymounted for slidable movement in said bore responsive to an outsideforce from either side of the bolt, spring means for resilientlyprojecting said actuating end portion from the bolt, said sear slidebeing provided with a recess for receiving said cam portion, a pair ofangularly related chordal portions having spaced-apart inclining wallsin said recess, said chordal portions being selectively cooperable withsaid cam portion for pivoting said sear to unlatch said firing memberwhen said sear slide is mounted for actuation from either side of thebolt, a lug on said sear cooperable with said sear slide for blockingsaid sear against movement away from latching cooperation with saidfiring member when said sear slide is in normal position and to bereceivable by a mortise in said sear slide when said cam portion is incooperating engagement with one of said inclining walls for pivotingsaid sear to unlatch said firing member and said actuating end portionis moved against said spring means, and an actuator member slidablymounted in a cylindrical hole in the bolt, said actuator being slidablyreceived by one of a pair of holes through said sear slide for securingsaid sear slide against rotation when mounted for actuation from eitherside of the bolt and for camming cooperation with said sear slide toactuate said sear slide from the top side of the bolt.

References Cited in the file of this patent UNITED STATES PATENTS1,981,855 Coupland Nov. 27, 1934 2,462,114 Lochhead Feb. 22, 19492,535,709 Weeks Dec. 26, 1950 2,562,801 Maillard July 31, 1951

